The structure of forest vegetation on industrial landfills of different ages

Abstract The purpose of the research is to describe plant community formation on the quarry surfaces to determine a path for optimal revegetation. To achieve the goal, the studies determined soil pH, the content of skeletal fraction, basal respiration, and performed the acidimetric assessment of CO2. The research program aimed to investigate the peculiarities of plant communities' formation in areas with different degrees of revitalization and investigate the influence of soil cover on plant associations. Results showed that the average basal soil respiration rate on the quarry was extremely low (about 0.3 mg CO2/g of soil/h). The CO2 content in the carbonate ranged from 0.07% to 0.7%, with the higher figures observed in older Kuzbass rather than Mosbass and Sokolovsky quarries. An analysis of soil samples from three quarries revealed four plant groups at sites associated with the prevalence of specific fractions, such as gravel, sand, silt, and stony soil. Given that Kuzbass is the oldest open‐pit mine, forest vegetation species dominate here in the surveyed areas (>40%), and this feature is typical of gravel soils. The dominant species present on the gravel substrate were downy birch (Betula pubescens), common hornbeam (Carpinus betulus), European oak (Quercus robur), Siberian spruce (Picea obovata), common juniper (Juniperus communis), Siberian larch (Larix sibirica), common pine (Pinus), and Siberian fir (Abies sibirica). Mosbass is also characterized by a diversity of similar species, though work on mineral mining there ended in 2009, more recently than in other sites. Stony and sandy soil fractions predominated in the Sokolovsky quarry, although other studied substrates were also present.


| INTRODUC TI ON
For centuries, quarries have served as vital mining sites, reshaping the landscapes they occupy. This process has changed the landscape of many regions. Scientists who investigate the issue of quarries claim that places changed by natural disturbances represent groups of rare biodiversity (Talento et al., 2020). Many geological faults become ecological corridors and spaces of communication, shelter, and biological transit, thereby ensuring the survival of certain biomes (Roberts & Mattoo, 2018;Talento et al., 2020). Therefore, the territories modified due to mining activities can create other biodiversity repositories. With proper planning, abandoned open pits can help create new habitats for flora and wildlife (Lameed & Ayodele, 2010;Talento et al., 2020).
These abandoned lands have low levels of biomass productivity and quantity of resources, due to extreme abiotic environmental conditions (Roberts & Mattoo, 2018). However, extreme conditions are becoming increasingly rare as humans attempt to increase the productivity of the land. The early successional phase, dominated by rare representatives of the flora, deserves special attention among researchers (Hattermann et al., 2018). Given that quarries are an important part of the country's economic activity, they can increase biodiversity in certain regions, which is especially important in densely populated areas .
The mining industry of our planet annually extracts more than 100 billion tons of raw materials, and only about 7%-8% is used effectively. This leads to the radical restructuring of the geological structure of the Earth's surface to a depth of several 100 m.
This change complicates or completely destroys the existence and functioning of organismal associations. The purpose of revegetation is to reproduce the productivity of the territories disturbed by the mining industry and return them to various types of use. This procedure involves the implementation of a complex of engineering, mining, meliorative, agricultural, and forestry works (Ramirez-Cruz et al., 2019).
Over the centuries-old history of mineral resource development, different-age quarry and dump landscapes have formed. Currently, they are at different stages of development. Some of them are revegetated, but most are self-regulating. Some of them can be classified as cultivated; they have long served as pastures and hayfields (Bartz & Kowarik, 2019).
Quarry and dump landscapes differ sharply from the surrounding zonal natural objects, as well as from other anthropogenically disturbed territories, due to a complex of specific plant growth conditions with contrasting ecological conditions and a special type of succession process. At the same time, human-made ecotopes most fully reveal the adaptive capabilities of many plant species. Starting from the first stages of overgrowth, along with the group of weeds, species from the composition of the surrounding flora take an active part in it (Kowarik, 2019).
The biological reclamation of industrial dumps requires a comprehensive study. The study can make it possible to implement appropriate evidence-based measures, in particular, the clarification of the natural overgrowth processes. An analysis of this process can determine possible ways of revegetation (Hölzel et al., 2016).
Biological conservation of the surface of dumps is an urgent task, as their natural overgrowth is slow, and the formed vegetation groups are low-productive (Skálová et al., 2015).
The natural vegetation of quarries and dumps depends on the following: 1. zonal and climatic conditions of the district, 2. the microclimate and physicochemical soil properties that determine the ecotopic selection of plants, 3. surrounding vegetation as a source of plant seed deposition on the barren surface of the dump.
In both natural and semi-natural habitats, soil vegetation and related physicochemical processes are the main components of terrestrial ecosystems (Comerford, 2005). The consistent availability of nutrients for plant growth is an important factor that controls the nutrient cycle in soils for the primary production of plant communities (Spohn, 2020). However, when used in agriculture or forestry, individual parameters are often insufficient to monitor soil degradation and desertification or perform effective reclamation of soil substrate in post-industrial territories. Factors affecting nutrient availability in soil are the first parameters to be considered when assessing soil quality and restoring substrate function while renovating ecosystem function (Skálová et al., 2015). Soil particulate fraction characteristics are the principal feedback indicators of the soil-vegetation system (Hölzel et al., 2016). Some researchers have studied several soil-vegetation relationships in more detail, including interactions between some tree species, desertification, and soil erosion (Wijitkosum, 2020).
In the scientific literature, there is a gap related to the knowledge of the relationship between soil physicochemical properties and vegetation functions that develop spontaneously in postindustrial zones (Pourbabaei et al., 2020). These relations include the regulation of water infiltration and its availability for a specific plant community, as well as for the whole ecosystem (Fischer et al., 2014). Most studies examine the role of particulate fraction and soil properties in post-industrial sites in the rehabilitation process (Fischer et al., 2014).
Several studies have analyzed the effect of the soil particulate fraction on the stability of the soil vegetation system due to regeneration processes (Halecki & Klatka, 2021). The significance of the fine fraction in soil processes has been demonstrated in numerous studies (Hölzel et al., 2016;Kowarik, 2019;Wijitkosum, 2020). Compared with soil in natural and semi-natural ecosystems, the relationship between soil particulate fractions, water, nutrient availability, and spontaneous feedback of vegetation in post-industrial sites is significantly more complex. This issue requires an analysis regarding practical restoration purposes.
The process of quarry regeneration is a relatively slow process, which can take years (Krüger et al., 2017). Limited nutrients and the physical condition of the soil are the main factors affecting the development of flora in areas of abandoned quarries (Fischer et al., 2014). A restored community must be capable of developing natural processes without human intervention (Hong et al., 2019).
In addition, a recovered ecosystem must resist stress and include a set of native species (Lugo, 2020). Plant species should grow in rock conditions, in soils with low nutrients and water content, in soils with very high or conversely low pH values, or in areas located on steep slopes. Due to soil disturbances in quarries, the succession of plants is slow, requiring up to several centuries, especially for forest vegetation. Therefore, it is necessary to evaluate all possible approaches to the restoration of abandoned quarries, taking into account changes in the ecological role and biodiversity of fauna.
Forest plantations are recognized as a powerful soil-forming factor that significantly affects the morphological structure, physicochemical and biological properties. When creating forest plantations, the focus is on the selection of an assortment of tree species that can increase the fertility of soil mixtures (Halecki & Klatka, 2021;Kowarik, 2019;Wijitkosum, 2020). They found that the added silt increases the amount of organic matter, consequently, successional plant species colonize renewal zones. Sewage sludge can be used as soil amendments (Carabassa et al., 2018). However, these additives often contain heavy metals that negatively affect the vegetation cover. In limestone quarries, ecological renewal of the biotope can take place within a few years after the use of backfill. Gentili et al. (2020) determined that soil granularity plays a key role in regeneration. The authors showed a linear dependence of the grass cover on the age of the renewable area of 3 × 3 m and the amount of organic and mineral matter. In addition, species diversity is affected by the stony composition of the soil and the sand content (Gentili et al., 2020).
Succession is crucial, especially for the renewal of grass cover, but its role is even more considerable regarding forest vegetation.
Therefore, it is necessary to study the influence of soils on the renewal of woody cover during natural renewal processes. This study employed a more general approach to evaluate the relationship between the size of soil particles in coal mine tailings and the diversity of forest vegetation that developed during spontaneous succession. Given that open-pit mines have significant differences, the purpose of this study was to investigate the vegetation and soil characteristics of quarries of different ages on the territory of the Russian Federation and the Republic of Kazakhstan. This procedure included the following tasks: 1. selecting open-pit landfills of different ages and climatic conditions to investigate the peculiarities of their soil formation, 2. identifying the main physical and chemical properties of the soil, 3. analyzing the baseline diversity of forest vegetation species for future comparison.

| Study regions
The studies took place on the territory of the Russian Federation in the Kuznetsk coal basin (Kuzbass) (55°21′16″N 86°05′19″E) The Sokolovsky quarry and its dumps are located within the boundaries of the Kostanay physical-geographic province. The territory of latter is a sloping undulating plain that gradually descends to the northeast, with absolute elevations of 150-200 m.
It belongs to the subzone of arid steppes on southern loamy, sandy, low-humus, and often saline chernozems. Its overgrowth depends on the edaphic properties of soil mixtures and mesorelief forms. The climate is strongly continental, with a pronounced four seasonal alternation. The mean yearly temperature is 2.8°C.
The ground cover here is primarily represented by dark brown and solonetz soils.
In addition to the previous locations, this research was also car- This area has a moderately continental climate, characterized by relatively warm summers and moderately cold winters. The landscape is dominated by forest-steppe and steppe. Soils are primarily represented by moderately thick chernozems.

| Sample selection
The experiment consisted of the following stages: 1. Establishing experimental plots; 2. Soil sampling and analysis; 3. Study of forest cover.
To determine the main forest inventory assessment indicators of the experimental forest stands, experimental trial areas were established. The procedure complied with the methodology of conducting field research using the field geographic information system Field-Map (IFER-Monitoring and Mapping Solutions. S.r.o., www. field -mappi ng.com). In field conditions, this methodology allows researchers to combine the formation of attributive and cartographic information about forest objects in a single technological process.
Given that small-scale topographic differences strongly influence the soil and vegetation succession process (Hong et al.,

| Statistical analysis
MANOVA (multivariate analysis of variance) was used to process the results. The analysis employed Microsoft Excel and Statistica 10 software packages. In the study, MANOVA was performed on a standardized data matrix to alternately test the qualitative variables available in the database. This program allowed the authors to calculate the parameters of species diversity. In addition, the study used a correlation analysis to relate the vegetation species composition with the size of soil particles and characterize the relationship between the floristic composition of forest vegetation areas and the measured physicochemical soil characteristics (Smith, 2018). The set threshold for statistical significance was p ≤ .05.

| Data use
Since species diversity may be exaggerated by the presence of rare  although work on mining minerals ended not that long ago (in 2009).
As for the Sokolovsky quarry, the stony and sandy soil fractions predominate, although there were other studied substrates, in particular silt ( Figure 5). The indices of diversity in Kuzbass were correspondingly higher than those in Mosbass and Sokolovsky quarries.
This fact is also associated with the structural and aggregate composition of the soil, in particular with lower silt content.

| DISCUSS ION
Soil substrate structure and lack of water and nitrogen have long been considered as probable reasons for difficulties in creating plant cover in highly industrialized regions (Dettori & Donadio, 2020;Smith, 2018). There is a common opinion that abiotic factors are the driving forces that shape the structure of the vegetation of many terrestrial ecosystems. The latter include those created in postindustrial and urban areas (Heip et al., 1998). this study (such as B. vulgaris and Q. ilex) were considered rare for the industrial regions of the Russian Federation (Fields, 2004).
The composition of the bedrock, which is the basis of coal mine landfills with plants, depends on the weathering process of waste lying in these landfills. In turn, they largely depend on the type of stored rock and its physicochemical properties (Qiu et al., 2018; Puijenbroek et al., 2019). We have found that the predominant fractions of particles were gravel, sand, and silt. They had differences in the quantitative and qualitative composition of forest vegetation.
The continuous process of alteration, the partial segregation of stone materials, and the development of plant succession constantly modify the proportion of certain soil particles in the soil substrate (Czerepanov, 1995). Due to the substrate's complex petrographic and granulometric structure in these landfills, soil processes are slow. Besides, the thickness of the hummus/organic layer can vary from a few millimeters (in the initial phase of succession) to several centimeters (in the later stages of succession). In shallow soil substrate layers, the size of soil substrate particles changes, along with the contents of some chemical compounds (Nguemezi et al., 2020).
The creation of new tree stands is well-known in restoration ecology (Castle et al., 2016;Lima et al., 2018;Poirier et al., 2020;Schoonover & Crim, 2015). This method of tree planting and associated maintenance require the allocation of significant resources. Nevertheless, they do not always produce satisfactory results, for example, when continued maintenance is required (Liu et al., 2020;Poirier et al., 2020). It implies the revegetation of industrial quarries that evolve through natural processes (e.g., colonization and succession).
When succession occurs, plants, which are typical for the surrounding area, are those that appear in quarries most often. Thus, Quercus pubescens, Fraxinus ornus, Acer campestre, as well as some exotic species, such as Pinus nigra, Acinos arvensis, and Malva ignoreta, were found in limestone quarries. They could appear as a result of changes in soil characteristics (Boscutti et al., 2017). At the same time, in China, the study of the vegetative processes of coal mine renewal revealed the presence of Ulmus pumila, Ailanthus altissima, P. tabuliformis, and P. simonii. This may be due to the fact that the acidity of soils after coal mining is significantly lower than that of limestone (Yuan et al., 2018).
In our study, the dominant species were B. pubescens, Q. ilex, and S. acutifolia, which are common in the territories adjacent to the quarries.
The activity of quarries is the complete removal of vegetation, which serves as a habitat and niche for wild animals. Only some serial or successional species, which are more adaptable, can take advantage of temporary and unstable situations. However, the complex manipulation of the environment in a quarrying project, directly or indirectly (habitat modification), will lead to serious consequences where rare and endangered species become maladaptive.
In this case, more adaptive species, whose numbers are smaller, are preserved due to pollution (Lameed & Ayodele, 2010). According to several authors, the protection of the quarry area creates a chance to increase the recreational area in order to combine industry and preserve the geological heritage. At the same time, it can contribute to the economic and social development of local communities. If managed well, this strategy can bring economic and social benefits to the region (Lugo, 2020;Talento et al., 2020).
Overcoming land degradation through integrated landscape management should become a priority in the policies of departments related to ecology and revegetation. The results of the present research have shown that the increase in the amount of organic matter in the soil composition is the main process of soil formation. It leads to the formation of layers with the maximum amount of organic matter in the accumulative ecotype with optimal substrate moisture regime and physical parameters. These processes form horizons with the maximum thickness and the highest organic carbon content in the accumulative ecotype with optimal substrate moisture conditions and physical parameters. The differences between the surface and underground horizons decreased with the overgrowth time. This change may be due to the high intensity of organic matter accumulation in the soil (Egli et al., 2018). Along with an increase in organic matter accumulation, the acidification and leaching of carbonates took place rather quickly. That was especially noticeable in the upper layer of the Kuzbass soil horizons rather than in other quarries. In some forests, such as small-leaved forests, soil formation processes are more rapid than in eluvial ecotypes (Czerepanov, 1995) (Dettori & Donadio, 2020;Gorozhanina et al., 2022).
The results in this work show that soil substrate structure influences species richness and the diversity of developing vegetation species.
There were significant differences in species richness and diversity in areas with a predominance of the stony fraction in the soil substrate compared to the silty fractions. In general, these indicators were at their highest values for stony and gravel substrates. Difficult habitat conditions on muddy substrates (low potassium content and irregular soil structure) have probably resulted in fewer species colonizing these habitats (the youngest Sokolovsky quarries) during vegetation development (Halecki & Klatka, 2021;Poirier et al., 2020).
The process of revegetation in quarries with different soil compositions has already been well studied. Most of the studies are devoted to various aspects of vegetation cover succession (Schoonover & Crim, 2015). Some studies have analyzed the soil formation processes in sufficient detail (Lugo, 2020). Thus, previous studies have long considered the structure of the soil substrate and the lack of water and nitrogen as probable causes of difficulties in creating plant cover on the territories of industrial facilities (Lugo, 2020;Van Puijenbroek et al., 2019). This conclusion was confirmed by the present research. Abiotic factors are generally believed to be the driving forces that shape the vegetation structure of many terrestrial ecosystems, including those created in post-industrial and urban areas (Qiu et al., 2018). This fact adds value to the research performed. However, the present work lacks comprehensive observations on soil and forest cover restoration and the relationship between these features.
Natural and semi-natural habitats, soil, vegetation, and their associated physicochemical processes require careful management to protect and proactively manage the long-term valuable landscape and cultural assets that society aims to preserve.

| CON CLUS IONS
The

ACK N OWLED G M ENTS
None.

FU N D I N G I N FO R M ATI O N
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

CO N FLI C T O F I NTER E S T S TATEM ENT
The authors have no competing interests to declare.

DATA AVA I L A B I L I T Y S TAT E M E N T
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